1. Field of the Invention
This invention relates to a recording medium suited for recording carried out using a water-based ink, and an image forming method and a printed material which make use of the recording medium. More particularly, it relates to a recording medium that may hardly cause beading, and an image forming method and a printed material which make use of such a recording medium.
2. Related Background Art
In recent years, ink-jet recording, which is a system used to record images, characters or letters and so forth by causing minute ink droplets to fly utilizing various types of drive mechanisms and adhere to a recording medium such as paper, has rapidly spread in various uses including information equipment as apparatus for recording various types of images, because of the features such that the recording can be performed at high speed and low noise, multi-color recording can be achieved with ease, recording patterns can be of great flexibility and neither development nor fixing is required. The ink-jet recording is also being widely put in practical use in the field of full-color image recording, because images formed by multi-color ink-jet recording can be recorded as images comparable to multi-color prints obtained by lithography or prints formed by color photography, and at a lower cost than those obtained by conventional multi-color printing or color photography, when a small number of printed materials are prepared. Recording apparatus and recording processes have been improved with progress in recording performances, e.g., with achievement of higher recording speed, higher minuteness and full-color recording. With regard to recording mediums, too, it has become required for them to have high-level properties.
To meet such requirements, forms of recording mediums have been hitherto proposed in great variety. For example, Japanese Patent Application Laid-open No. 55-5830 discloses an ink-jet recording paper provided on the surface of its support with an ink-absorptive coat layer. Japanese Patent Application Laid-open No. 55-51583 discloses an example in which noncrystal silica is used as a pigment in a coating layer; and also Japanese Patent Application Laid-open No. 55-146786, an example in which a water-soluble polymer coat layer is used.
In recent years, a recording medium having a coat layer formed using an alumina hydrate of Boehmite structure, as disclosed in, e.g., U.S. Pat. No. 4,879,166 and U.S. Pat. No. 5,104,730 and Japanese Patent Applications Laid-open No. 2-276670, No. 3-275378, No. 3-281384 and No. 5-32037.
As also disclosed in U.S. Pat. No. 4,374,804 and U.S. Pat. No. 5,104,730 and Japanese Patent Applications Laid-open No. 58-110287, No. 1-97678, No. 2-276671 and No. 4-37576, it is also proposed to form an ink receiving layer of multi-layer construction by the use of a silica or alumina material.
All the proposals, however, are concerned with improvements of ink absorptivity, resolution, image density, color performance, color reproducibility, ink adsorptivity, transparency and so forth. Even such proposals bring about no improvement or settlement good enough to be satisfactory in respect of beading.
Especially when a large quantity of ink is imparted at one time to substantially the same portion of a recording medium as in the case of high-speed full-color recording, it is difficult to prevent the beading well enough to be satisfactory.
According to a finding of the present inventors, the prior art recording mediums have proved to cause beading when subjected to printing which imparts 30 ng of ink at 32.times.32 dots per 1 mm.sup.2.
Herein, the beading refers to a phenomenon that occurs because of an insufficient ink absorptivity of recording mediums and is, after printing, visually recognized as color uneveness shaped like beads.
With regard to the ink absorptivity, its improvement has been made in the above prior art from the viewpoint of pore volume and pore radius, but there is no disclosure as to the beading. Also, the problem of beading can not be well settled if only both the pore volume and the pore radius are taken into account.
For example, U.S. Pat. No. 5,104,730 and Japanese Patent Applications Laid-open No. 2-276670, No. 2-276671 and No. 3-275378 disclose a recording medium having a narrow pore size distribution of 1.0 to 3.0 nm as average pore diameter. Such pore size distribution is attributable to good adsorption of dyes, but can not provide sufficient solvent absorptivity to tend to cause beading.
Japanese Patent Application Laid-open No. 3-281384 also discloses an alumina hydrate that has the shape of columns with an aspect ratio of 3 or less and forms hair-bundlelike assemblages oriented in a given direction, and a method of forming an ink-receiving layer having good ink absorptivity and color performance by the use of such an alumina hydrate. However, since particles of the alumina hydrate are oriented and densely packed, the gaps between particles of the alumina hydrate in the ink-receiving layer tend to be narrow. Hence, there is the tendency that the pore diameter is one-sided toward the narrow side and the pore size distribution is narrow.